This invention relates to an optical system for the accurate monitoring of position and orientation.
Systems that measure or monitor the position and orientation of an object are important computer input devices. For example, computer monitoring of position and orientation of a user's head is required in some virtual reality systems, and is also used in some heads-up display systems. Such input devices are also useful in the manipulation of computer graphics displays, and in motion capture systems that record the movement of a person or some object.
The speed and accuracy of a position and orientation monitoring device is of critical importance in many applications. For example, virtual reality systems, in which the user is presented with a computer-generated environment through a head-mounted display, require continuous monitoring of the orientation of the user's head, updated at a rate that is fast enough to maintain the illusion of reality. Further, heads-up display systems in which information is merged with the user's visual field of view, for example, a transparent head-mounted display for a surgeon that shows the location of internal features (from X-rays or CAT scans) of a patient undergoing surgery, also require a high degree of accuracy in the continuous monitoring of the orientation of the user's head.
A number of different systems have been developed to measure position and orientation. Systems typically include devices that utilize ultrasonic emitters and detectors, or that sense magnetic field direction, or devices, such as CCD cameras, that detect images. The accuracy and speed of each system have certain limitations peculiar to its particular design. Systems capable of a high degree of accuracy and speed have been constructed, but these systems generally require the use of a complex device and costly components.
A system that accomplishes position and orientation monitoring through the sensing of scanned beams is shown by Morrison, U.S. Pat. No. 5,187,540. This system employs at least three light sensors (or emitters) and a scanning optical device that produces a pair of planar, fan-shaped, scanning light (or acceptance) beams. These beams are incident to the frame of reference from different directions, the planes of the beams being inclined to one another. The timing of the light sensor signals is processed by a computer to calculate the position and orientation of the object.
A different system, described in DiMatteo et al., U.S. Pat. No. 4,396,945, uses three light sensors (or sources or reflectors) and two optical scanners (projectors or cameras) to monitor the position and orientation of an object. Each of the three light sources, sensors, or reflectors are controlled to distinguish their respective signals. In one embodiment, one optical scanner produces a fan-shaped, planar beam that scans in only one direction, while the other scanner produces a pattern that scans in two perpendicular directions.
Another system, described in DeMenthon, U.S. Pat. No. 5,388,059, uses a single camera and at least four light sources on an object to monitor the position and orientation of the object. DeMenthon also describes an iterative computation of a 4.times.4 transformation matrix representing the pose of the object that provides high positional accuracy using this relatively simple design.